In the mid 1990's it became obvious that the world-wide consumer appetite for bandwidth hungry applications would eventually mean a shift not only in the consumer electronics that deliver the “experience,” but also in the way that access networks would be deployed and used. At the time, while advances in data delivery over legacy copper networks (DSL for instance) and the implementation of hybrid-coaxial deployments seemed to suffice it was clear that in a short time both of these methods would have severe shortcomings to available end line customer applications. By the early years in this decade, the accelerated availability of high definition television programming, video-on-demand, VoIP, peer to peer gaming, IM, video uploading, etc, made the need for improved access immediate. Computer networks have evolved to the extent where they are coupled to subscriber television systems for the delivery of multi-media entertainment, including audio and video. Likewise, subscriber television systems offer broadcast signals carrying information broadcast to a wide audience (e.g., content from CBS, NBC, ABC, HBO, etc.) and narrowcast signals carrying context or destination-specific information (e.g., video-on-demand, web-data, etc.). In other words, narrowcast signals are directed more specifically or selectively to individuals or groups of subscribers. Further exacerbating the demand for fiber and narrowcast bandwidth is the demand for localized and customized programming that is specific to a subset of users, or even single users.
Optical and hybrid networks were developed to satisfy the growing appetite for bandwidth and speed. For instance, in subscriber television systems, among other networks, hybrid fiber/coaxial (HFC) network infrastructures have been developed to create a broadband network to handle a wide range of information. In a subscriber television system utilizing HFC, a forward path (e.g., from a headend to subscribers) carries information through a network of optical and cable mediums and corresponding components and equipment. A return path is also typically established, whereby data from each subscriber terminal (e.g., set-top box) can be carried back to the headend. However, the demand for bandwidth and speed has eclipsed the rate at which fiber plant can be installed. In order to overcome this challenge, multiplexing systems were developed that allowed multiple optical signals to be carried simultaneously over a single fiber, thus reducing the demand for additional fiber strands. Multiplexed signals are generally demultiplexed at a node.
Typically, a node is included in the forward path to act as a point of distribution for signals received from the headend, and as a point of consolidation for a plurality of subscriber terminals sending signals back to the headend. Nodes may be “partitioned” logically to segment the node into a plurality of subgroups, each subgroup responsible for feeding information to and receiving information from a plurality of subscriber terminals. For instance, narrowcast signals, given the selectivity in intended destinations, are often demultiplexed at the node, and channeled to the logical segment to be forwarded to the intended destination.
Several techniques have been employed in the past to provide narrowcast and broadcast signals over an optical network. One method involves the use of a broadcast transmitter residing at the headend to deliver broadcast signals and a plurality of narrowcast transmitters multiplexed at the headend to deliver narrowcast signals. The broadcast transmitter can be an externally modulated or directly modulated optical transmitter located at or near the dispersion zero wavelength of the optical fiber. The narrowcast transmitters generally comprise high launch powers (e.g., >8 dBm) and utilize a dense wavelength division multiplexed (DWDM) ITU spectrum in the “C” band to reduce nonlinear crosstalk due to high launch powers. The broadcast and narrowcast signals are carried along the optical medium and received at a receiver residing at the node, the receiver combining the broadcast and narrowcast signals. The receiver generally comprises a photodiode that receives and converts the optical signal to an electrical signal for further processing.
Some limitations to such a conventional approach include the use of the DWDM spectrum in which the launch powers are high, which may increase the risk of non-linear cross-talk at large wavelength differences. Furthermore, crosstalk and distortion can also preclude the use of coarse wavelength division multiplexing (CWDM).
Therefore, what is needed are systems and methods that overcome challenges found in the art, many of which are described above